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Original thinker redefines bioreactor control
The incredible power and intelligence available from today's most elementary PLCs has been captured by a self-taught control engineer, who is using them to manage the growth of cell cultures in bioreactors. Lee Pettitt of I4Innovation in Thetford has married four Mitsubishi Electric Alpha controllers with the massively powerful GT15 HMI from the same company to constantly monitor and adjust pumps, propellers, inlet and outlet valves and multiple sensors in the reactors. In a parallel process, the control system also manages the production of nitrogen and oxygen from atmosphere for use in the reactor.
He gives some background: "Cell cultures are vital in many fields of modern medicine, from pharmaceuticals to skin grafts and organ transplants, dialysis and high intensity neonatal procedures. There are four basic types of culture: insect, mammalian, yeast and E.Coli, each with literally thousands of variations to meet specific needs for individual cases."
Lee's system can store precise recipes on the HMI, which are also used for real time process control and comprehensive data logging and Digital Signature Management to meet the stringent requirements of International Standard CFR21 part 11.
In use, the various components of the chosen recipe are introduced to the reactor via inlet valves and are circulated through an aqueous media at an optimal rate to promote growth of the culture. Temperature is usually critical and sometimes pressure, dissolved oxygen, pH are too. Usually oxygen, nitrogen or carbon dioxide is introduced at a controlled rate in order to promote growth. Impellers keep the solution circulating and measurements are taken from several monitoring points to constantly check on conditions for growth. Temperature, pressure and exposure to light can also be monitored and adjusted.
Beside the reactors, a Pressure Swing Absorption system can be activated to separate and compress nitrogen and/or oxygen from the atmosphere for use in cell growth. "Most other bioreactors use bottled gases," Lee explains, "but this leads to an extra cost, plus a considerable bottle management effort. This gives users of our equipment a distinct advantage, although we still have to use bottles for carbon dioxide."
The bioreactors have 32 inputs and 24 outputs, plus eight analogue outputs, all achieved with Mitsubishi Alpha mini controllers. Most people expect to see a far larger rack PLC at the heart of the control system and so are delighted with the simplicity of the hardware. They recognise that it is far less costly to buy, to run and maintain and easier to reconfigure if user requirements change. Lee again: "I discovered Alphas about six years ago and now hardly ever use anything but. When used to their full capacity they are very powerful, and every succeeding new version is even more powerful. There is a clarity to the way they are programmed and I have converted several older control systems from larger PLCs to Alphas - usually improving performance and certainly never compromising it."
Part of his success is due to the fact that he often uses them in conjunction with a state of the art HMI, as is the case with the bioreactors. "HMIs are very versatile and can be a powerful addition to a control system. I work hard to develop user-friendly graphics with them, trying to see the machine operation and process sequence from the operator's point of view, rather than from the control system developer's position. This can require some mental gymnastics on my part, but there are some tricks of the trade - like letting the potential operators tell me what they want, rather than me trying to explain the systems to them."
In fact, the HMI is often the key selling point for Lee and his colleagues. I4Innovation make the bioreactors housings in-house using a fabrication technique, rather than buying in moulded ones. "We put the HMI in a separate housing, which is pivot mounted to the main housing so that operators can adjust the viewing angle. It's a little point, but every potential customer nearly always comments favourably on it."
Like the Alphas, the HMIs get steadily better and Lee is currently assessing the new generation Mitsubishi GT16, which has, amongst other advances, a massive memory and high resolution screen. "We are going to do a video version of the user manual and embed it into the GT16," says Lee. "This will allow bioreactor operators complete autonomy, so in theory anybody will be able to plug them in and teach themselves everything they need to know."
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